The manufacture of insulating products based on mineral wool generally comprises a stage of manufacture of the wool itself, which can be carried out by various processes, for example according to the known technique of fiberizing by internal or external centrifugation. The centrifugation consists in introducing the molten mineral material (glass or rock) into a centrifugal device comprising a multitude of small orifices, the material being projected towards the peripheral wall of the device under the action of the centrifugal force and escaping therefrom in the form of filaments. On leaving the centrifugal device, the filaments are drawn and carried towards a receiving member by a gas stream having a high temperature and a high speed, in order to form a web of fibres (or mineral wool) there.
In order to provide for the assembly of the fibres together and to make it possible for the web to have cohesion, a sizing composition comprising a thermosetting resin is projected onto the fibres, on the route between the outlet of the centrifugal device and the receiving member. The web of fibres coated with the size is subjected to a heat treatment, at a temperature generally of greater than 100° C., in order to bring abut the polycondensation of the resin and to thus obtain a thermal and/or acoustic insulating product having specific properties, in particular dimensional stability, tensile strength, thickness recovery after compression and homogeneous colour.
The sizing composition to be projected onto the mineral wool is generally provided in the form of an aqueous solution including the thermosetting resin and additives, such as a catalyst for the crosslinking of the resin, an adhesion-promoting silane, a dust-preventing mineral oil, and the like. The sizing composition is generally applied to the fibres by spraying.
The properties of the sizing composition depend largely on the characteristics of the resin. From the viewpoint of the application, it is necessary for the sizing composition to exhibit good sprayability and to be able to be deposited at the surface of the fibres in order to efficiently bind them.
The resin has to be stable for a given period of time before being used to form the sizing composition, which composition is generally prepared at the time of use by mixing the resin and the additives mentioned above.
At the regulatory level, it is necessary for the resin to be regarded as non-polluting, that is to say for it to comprise—and for it generate during the sizing stage or subsequently—as little as possible in the way of compounds which may be harmful to human health or to the environment.
The thermosetting resins most commonly used are phenolic resins belonging to the family of the resols. In addition to their good crosslinkability under the abovementioned thermal conditions, these resins are soluble in water, have a good affinity for mineral fibres, in particular glass fibres, and are relatively inexpensive.
These resols are obtained by condensation of phenol and formaldehyde, in the presence of a basic catalyst, in a formaldehyde/phenol molar ratio of greater than 1, so as to promote the reaction between the phenol and the formaldehyde and to reduce the level of residual phenol in the resin. The condensation reaction between the phenol and the formaldehyde is carried out while limiting the degree of condensation of the monomers, in order to avoid the formation of long, relatively water-insoluble, chains which reduce the dilutability. Consequently, the resin comprises a certain proportion of unreacted monomer, in particular formaldehyde, the presence of which is undesirable because of its known harmful effects.
For this reason, resol-based resins are generally treated with urea, which reacts with the free formaldehyde by trapping it in the form of nonvolatile urea-formaldehyde condensates. The presence of urea in the resin in addition brings a certain economic advantage as a result of its low cost because it is possible to introduce it in a relatively large amount without affecting the operating qualities of the resin, in particular without harming the mechanical properties of the final product, which significantly lowers the total cost of the resin.
Nevertheless, it has been observed that, under the temperature conditions to which the web is subjected in order to obtain crosslinking of the resin, the urea-formaldehyde condensates are not stable; they decompose with restoration of the formaldehyde and urea, in its turn at least partially decomposed to give ammonia, which are released into the atmosphere of the factory.
Regulations with regard to environmental protection, which are becoming more restrictive, are forcing manufacturers of insulating products to look for solutions which make it possible to further lower the levels of undesirable emissions, in particular of formaldehyde.
Solutions in which resols are replaced in sizing compositions are known and are based on the use of a carboxylic acid polymer, in particular an acrylic acid polymer.
In U.S. Pat. No. 5,340,868, the size comprises a polycarboxylic polymer, a β-hydroxyamide and an at least trifunctional monomeric carboxylic acid.
Provision has been made for sizing compositions comprising a polycarboxylic polymer, a polyol and a catalyst, which catalyst is a phosphorus-comprising catalyst (U.S. Pat. No. 5,318,990, U.S. Pat. No. 5,661,213, U.S. Pat. No. 6,331,350, US 2003/0008978), a fluoroborate (U.S. Pat. No. 5,977,232) or else a cyanamide, a dicyanamide or a cyanoguanidine (U.S. Pat. No. 5,932,689).
A description has also been given of sizing compositions comprising an alkanolamine including at least two hydroxyl groups and a polycarboxylic polymer (U.S. Pat. No. 6,071,994, U.S. Pat. No. 6,099,773, U.S. Pat. No. 6,146,746) in combination with a copolymer (U.S. Pat. No. 6,299,936).
In US 2002/0091185, the polycarboxylic polymer and the polyol are used in amounts such that the ratio of the number of equivalents of OH groups to the number of equivalents of COOH groups varies from 0.6/1 to 0.8/1.
In US 2002/0188055, the sizing composition comprises a polycarboxylic polymer, a polyol and a cationic, amphoteric or nonionic surfactant.
In US 2004/0002567, the sizing composition includes a polycarboxylic polymer, a polyol and a coupling agent of silane type.
In US 2005/0215153, a description is given of a size formed by a prebinder comprising polymer of carboxylic acid and of a polyol, and from a dextrin as cobinder.
Furthermore, an adhesive composition based on heat-crosslinkable polysaccharides which can be used as size for mineral wool is known (U.S. Pat. No. 5,895,804). The composition comprises a polycarboxylic polymer having at least two carboxylic acid functional groups and a molecular weight at least equal to 1000 and a polysaccharide having a molecular weight at least equal to 10 000.